There are about a thousand normal ways for road water, rain, and condensate to get between the underbelly and the physical underside of the trailer. Doesn't mean you have a leak or some other insidious problem that must be corrected.
The drain will allow this water to avoid being trapped in there.
Every time you use an apostrophe to make a word plural, a puppy dies.
RV: 2018 Rockwood Mini Lite 2504S
TV: 2019 F-350 Lariat 4WD CCSB 6.7 PSD 3.55, 3,591 lb payload
Former RV: 2007 Fleetwood/Coleman Utah
Former TV: 2005 F-150 King Ranch 4WD SCrew 5.4L Tow Package